System virtualization creates multiple virtual systems from a single physical system. The physical system can be a stand-alone computer, or alternatively, a computing system utilizing clustered computers and components. Virtual systems are independent operating environments that use virtual resources made up of logical divisions of physical resources such as processors, memory and input/output (I/O) adapters. System virtualization is typically implemented through hypervisor technology. Hypervisors, also called virtual machine managers, use a thin layer of code in software or firmware to achieve fine-grained, dynamic resource sharing.
The hypervisor provides the ability to divide physical system resources into isolated logical partitions (also referred to as LPARs). Each logical partition operates like an independent system running its own operating environment (i.e., a virtual system). The hypervisor can allocate dedicated processors, I/O adapters, and memory to each logical partition. The hypervisor can also allocate shared processors to each logical partition. More specifically, the hypervisor creates virtual processors from physical processors, so that logical partitions can share the physical processors while running independent operating environments.
In addition to creating and managing the logical partitions, the hypervisor manages communication between the logical partitions via a virtual switch. To facilitate communication, each logical partition may have a virtual adapter for communication between the logical partitions, via the virtual switch. The type of the virtual adapter depends on the operating environment used by the logical partition. Examples of virtual adapters include virtual Ethernet adapters, virtual Fibre Channel adapters, virtual SCSI adapters, and virtual serial adapters.
Virtual adapters are often implemented through a Virtual I/O Server (VIOS). A VIOS manages physical I/O adapters (Fibre Channel disks, Ethernet, or CD/DVD optical devices). Other logical partitions controlled by the hypervisor are considered “clients” or Virtual I/O Clients (VIOCs) to the VIOS. The VIOS provides virtual Fibre Channel adapters and shared Ethernet capability to client logical partitions. The VIOS allows logical partitions to access SAN disks (or resources) using virtual Fibre Channel adapters mapped to a physical adapter which supports N_Port ID Virtualization (NPIV).
A storage area network (SAN) is a dedicated network that provides access to consolidated block-level data storage. SANs are primarily used to make storage devices, such as disk arrays, tape libraries, and optical jukeboxes, access to servers so that the devices appear like locally attached devices to the operating system. A SAN typically has its own network of storage devices that are generally not accessible through the local area network by other devices.
One of the activities in a complex environment is the transfer of a migration of one logical partition to another logical partition. Two reasons for a migration include: resource balancing and a logical partition does not have enough resources while another system does.